Homeostatic sleep response to naps is similar in normal elderly and young adults

Delta homeostatic regulation can be challenged by reducing delta need with daytime naps and measuring delta in post-nap sleep. We previously demonstrated that, after a late afternoon nap, young adults reduce the amount of delta in post-nap sleep by the amount in the nap. We compared homeostatic responses of 19 young adults (mean age 22.4 years) and 19 normal elderly subjects (mean age 71.4 years). Each participated in four separate 2-day sessions that consisted of a baseline night, a nap, and post-nap sleep. Nap times were 0900, 1200, 1500 and 1800 h. The 1800 h nap contained the largest amount of delta and produced the largest reduction in post-nap delta. The young and elderly groups respectively produced 28 and 24% of baseline delta in the 1800 h nap. Both groups showed equivalent delta regulation, reducing post-nap delta by 28 and 25%, respectively. In both age groups, the decrease in post-nap delta resulted from a reduced rate of delta production (power/min) and reduced non-rapid eye movement (NREM) sleep duration. Period-amplitude analysis showed that the reduction in power/min resulted from decreases in delta wave amplitude and incidence. None of the responses to nap challenges differed significantly across age groups nor were there gender differences or age by gender interactions. These results show that delta homeostatic responses to naps in the elderly parallel those of young subjects. REM sleep showed no homeostatic reductions following naps in either group. We believe that the striking differences in the delta and REM responses point to different biological roles of the two kinds of sleep.